This volume contains the lectures presented at the summer school “Diagnostic Tools for the Atmosphere”. The School was held in the framework of the International School of Physics E. Fermi of the Italian Physical Society in the period June 22–July 2, 1993, and in three years was the second school dedicated to the atmospheric sciences. The intention this time was to address a number of both experimental techniques and methods for the data treatment introduced in the last ten years or so in different fields of the atmospheric sciences. Considerable emphasis has been given since their introduction to the use of satellites or spaceborne measurements with a recent example being the important results obtained with DARS. On the other hand, less costly but key techniques dealing with remote sensing or in situ sampling have been introduced during the years. Of particular interest are the airborne instruments developed for the stratospheric measurement campaign organized by the NASA since 1976 to study the ozone hole and followed later by similar experiments to study the high-latitude ozone depletion in the northern hemisphere. The results of these experiments have helped clarify the role of chlorine-bearing compounds in the ozone depletion and the effect of the heterogeneous processes.

Another important development deals with the application of radar techniques to the study of the atmosphere. In particular the “wind profiler” can now be used to monitor continuosly the tropospheric winds, while other versions are able to study the convective processes in the boundary layer. The lidar can be also regarded as a radar even if its use in the visible or UV wavelengths has rather wide application.

The direct sampling of the atmosphere or the point measurements require new methods to analyse the data which are based mainly on the conservation properties of air parcels, potential temperature and potential vorticity. This method has forced the stratospheric dynamicists to rely heavily on the meteorological data assimilated in the few centres which have a global coverage (i.e. NMC and ECMWF).

Another challenge comes from the comparison of a large number of data obtained with different instrumentation and in a quite different condition. The above-mentioned “trajectory method” also deals with this problem which requires a rather accurate analysis of the data and the characteristics of different instruments.

The volume is quite arbitrarily organized in four chapters: the first three divide the different techniques according to the location of the measuring instrumentation (ground, air and space) with the fourth chapter dealing with theory and analysis.

For the gound-based techniques G. H. Mount and J. W. Harder report on the long-path absorption technique to measure OH, which is a rather important atmospheric minor constituent, but very difficult to measure. R. L. De Zafra has pioneered the CIO measurements from the ground using millimetre wave spectroscopy and reviews the basic principle of this technique.

J. C. Wilson and D. W. Fahey are among those who have developed airborne instrumentation for the ER-2 which has been mentioned in the introduction. They report on the sampling of aerosols and gases in the lower stratosphere. W. H. Brune may be regarded as another component of the same group and has learned his trade at Prof. Anderson's school. Brune has two contributions dealing with the instrumentation based on the resonance fluorescence of the most important radicals for the stratospheric chemistry. The first contribution reviews the airborne instruments used in the NASA campaign, while the second lecture with P. S. Stevens and J. H. Mather reports on a new development for an instrument to measure tropospheric OH and HO₂.

A. J. Krueger has developed and assessed over the years the capability of the TOMS instrument to measure ozone. In his contribution he reports on the extended capability of the same instrument to measure SO₂, which is the precursor of stratospheric aerosols which are formed following large volcanic eruptions. P. J. McCormick and P. H. Wang report on the results collected with the SAGE and SAM spaceborne instruments. These are rather inexpensive instruments and their results are now one of the main reliable databases to assess the global ozone and aerosol trend. The instrumentation developed by B. Carli has been flown only on stratospheric balloons. However, it is original enough that a quite sophisticated (even if unlucky) satellite instrument (SAFIRE) is based on it. The technique described here is used to measure in emission the spectroscopic features of many important atmospheric minor constituents in the far infrared (from 30 to 300 μm).

Meteorology has been one of the fields which has benefitted from the spaceborne instrumentation since the beginning of the “space era”. The closing chapter starts with a contribution by A. J. Miller on the comparison of data taken with different instrumentation. The quality assessment is essential to the use of the same data for the possible detection of the trend in ozone and temperature. An example of an application of this kind is given by R. S. Stolarsky for the ozone trend analysis. M. R. Schoeberl and L. L. Sparling report on the latest development of the trajectory calculations and conservative-property application with a rather impressive example of the power of this method. F. Einaudi finally gives an extensive review of the problems posed by the gravity waves on the prediction of severe weather.

Some contributions planned for this school are missing from this volume. L. Froideveaux was the author of a number of lectures on microwave sounding from space which were included in the course for completeness. Their content, however, is very similar to the lecture by J. Waters appearing in the E. Fermi School Proceedings of 1991 on the EOS program.

The volume also misses the contributions of G. FEA (on the impact of satellite measurements on meteorology) and G. Fiocco on the lidar technique. Unfortunately we had to compromise between a delayed volume and its incompleteness, and we thought that there is no sense in waiting too much before the lectures become obsolete.

The directors of the school would like to acknowledge the financial support to the school from ENEA, Istituto Nazionale di Geofisica and Agenzia Spaziale Italiana. This support helped to have in Varenna some of the main international experts whose lectures were very much appreciated by the students. The Varenna environment was gorgeous as usual and provided the right atmosphere in which lecturers and students could interact productively. As in the previous occasion the organization of the school was superb and E. Mazzi and her staff helped in every way they could. C. Vasini waited patiently also this time for those contributors who are always too busy. The President of the Italian Physical Society, Prof. R. A. Ricci, was very supportive in having after two years another school on atmospheric physics.

G. Fiocco and G. Visconti